1. Field of the Invention
The present invention pertains to drilling bits, and, more particularly, to instrumented drilling bits.
2. Description of the Related Art
As drilling technology matures and drilling operations become more complex, various types of sensors and other electronic components are being employed down-hole. Even drill bits, where the actual cutting occurs, are being equipped with electronics to improve or monitor their performance. Such bits are sometimes referred to as “instrumented bits.” For example, pressure transducers can be placed on the bit in order to obtain an overall pressure pattern experienced during drilling. This information may indicate, for instance, whether bit balling occurs which can significantly downgrade a bit's performance during drilling operation. Usually several types of sensors are implemented on a bit so that different parameters can be measured simultaneously. This can result in a detailed measure of the bit's performance during drilling that can be transmitted up the drill string to either the surface or a sub-assembly for storage. The positions of these sensors on the bit may vary, but multiple wires from each transducer transmit information up the drill string. Conventionally, this was implemented using a multi-pin connector with strict size limitations. The size limitations also limited the number of wires that could be connected.
One approach to this problem is employs digital multiplexers and digital circuitry down-hole. The information is handled digitally because digital data is relatively high quality. Data converted to a digital stream is more immune to noise than is analog data because there are essentially only two states that the data can take on, 1 or 0; these states can be represented by easily discernable voltages such as 5V and 0 V for example (actual voltage levels depend on power supply requirements). It is much easier to retain the integrity of digital data that has only two possible values than data spanning over a continuous voltage range such as in an analog waveform.
On the other hand, an analog waveform traveling over one or more conductors for any significant distance (depending on environment, this distance may vary), will get noise coupled on top of that waveform and potentially corrupt the data being transferred. An application such as an acquisition tool with analog sensors will typically install analog-to-digital converters and digital multiplexers in very close proximity to the sensors. This ensures that the analog waveform does not have to travel very far before getting converted to digital format, hence minimizing the chance of picking up noise.
By installing sensors as close as possible to the cutters on a bit, one is able to more accurately measure various effects during drilling. But space is a premium when it comes to bit designs, and so one of the biggest challenges with an application “on-the-bit” is finding room to mount electronics and install conductors. There is a delicate balance between implementing as much circuit functionality as possible while retaining the design structure of the drill bit to ensure high quality drilling. Thus, the conventional approach to analog components in down-hole applications is fraught with difficulty when applied to bits since it adds an extra electronic component (the A/D converter) as well.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.